Process for preparing 2, 5-dimethyl-2, 4-hexadiene



karma! 2,910,520 Patented Oct. 27, 1959 PROCESS FOR PREPARING2,5-D]1VIETHYL-2,4-

HEXADIENE Howard R. Guest, Charleston, Ben W. Kilt, Oua, and

Harry A. Stansbury, Jr., South Charleston, W. Va., assiguors to UnionCarbide Corporation, a corporation of New York "No Drawing. ApplicationFebruary 20, 1957 Serial No. 641,235

14 Claims. (Cl. 260-681) This invention relates to novel processes forthe preparation of 2,5-dimethyl-2,4-hexadiene. More particularly itrelates to methods for preparing 2,5-dimethyl- 2,4-hexadiene frommethacrolein and certain novel intermediates obtained thereby.

Heretofore it has been suggested to prepare 2,5-dimethyl-2,4-hexadieneby treating methallyl chloride with magnesium dissolved in a suitablemedium such as ethyl ether to form 2,5-dimethyl 1,5 hexadiene. Thisproduct was then converted to 2,5-dimethyl-2,4-hexadiene bytreatmentwith a suitable acid catalyst in liquid phase or chromealumina, for example, in vapor phase.

The reaction of magnesium in ethyl ether with methallyl chloride or thereaction of metallic sodium with isocrotyl chloride is, however, ahazardous procedure when undertaken on a scale suitable for commercialpurposes. A further difiiculty exists in that the expensive metalsemployed' were converted to the chlorides which have virtually no value.

We have now discovered, unexpectedly, that 2,5- diniethyI-ZA-hexadih canbe prepared by alternative processes from methacrolein, a relativelyinexpensive starting material. These processes involve a series ofsteps, the reactions of which are described as follows:

PROCESS 1 Step 1 Methacrolein is caused to react by heating attemperatures of approximately 140 C. to 225 C. and preferably at 150 C.and underautogenous pressure e.g., 500 pounds per square inch (p'.s'.i.)to form methacroleindimer (3,4- dihydro-2,5-dimethyl-2-forrnyl-2H-pyran), which when hydrogenated with Raneynickel catalyst at temperatures of approximately 80 C. to' 160 C. andunder pressure of 100 pounds per square inch (p.s.i.) to 1 000 p.s.i.

2 forms 2,5 dime'thyltetrahydropyran 2 methanol. It should be noted thata preferred hydrogenation temperature is C. with a pressure ofapproximately psi. This reaction can b'edes'cribed graphically in thefollowing manner.

CH1 (1H, OHg-O CH, 2on,=o ono /OH m'et haerolizi" HC\ o H: 0 CH0 Raney3,4-dlhydro-2,5-dimethyl- Nickel 2-tormyl-2H-pyran (methacrolein dimer)Cg: CH 'CE CH:

CH, CE; /G\ Y 2,5-dimethylttrahydro pyran-2-methano1 Step 2 A novelcompound,- 1,6-diacetoxy--2,5-dimethyl-2- hexen'e is prepared froml,2,6-triacetoxy-2, 5*dimethyl hexane by the release of acetic acidtherefrom. 1,2,6- triacetoxy-Z,S-dimethylhexane is" prepared directly bythe treatment of 2,5-dimethyltetrahydropyran-Z-methanol from Step 1,with acetic anhydride anda. Lewis acid or strong mineral acid such as,for example, aluminum chloride, boron trifluoride, z"inc chloride,sta'r'mic chloride, sulfuric acid, phosphorous pentoxide, nitric acid orphosphoric acid as a catalyst therefor at elevated temperatures, e.g.,140 C. to C. Further novel compounds resulting from this same reactionin small quantitative amounts are2,5-dimethyltetraliydropyraii-2-niethan01 acetate and l,2,6tiiacetoxy-Z,S-diniethylhexane. Further reaction of these lattercompounds by further heating with acetic anhydride and a Lewis acid orstrong mineral acid will result in their conversion to the desireddiester, 1,6-diacetoxy-Z,5-dimethyl 2-hexane. This is il lustrated bythe following schematic equation:

O H g HC-O- --CH H g H('JO- --OH; acetic anhydride OHF' o c 2011 00011afg fg H acetic acid (311,

HCCH; O on,- H 0 1 I l C-O-C-CH CH0CCH; H, H 1,6-diacetoxy-1,2.6-triacetoxy- 2,5-d1rnethyl-2- 2,5dimethylhexane hexane aceticanhydride+eatalyst 1 140 o.-1eo o. l Us; 0%; OHg-Cfi CH, (Em-C CH1 CH3CH3 ,9 w i1 O CHQOH 0 CHOCH; 8 ,5-dimethyl-2,6-dimethyltetratetrahydropymnhydropyran-Z-methanol e 2-methano1acetate 1 no \aeetic anhydrlde 2% cata r 140 o.-1eo 0. o 3 a ll :5GOCCH; g

l? H CC-O-CCH;

H H C-C-H fl) (k-O-C-CH; Ha 1,2,6-trlaeetoxy- I 2,5-dtmethylhexane Step3 Step 4 The 1,6-diacetoxy-2,5-dimethyl-2-hexene from Step 2 is thenhydrogenated with a Raney nickel catalyst under autogenous pressuree.g., 150 p.s.i. at C. to 65 C. and preferably C. This reaction resultsin the formation of about sixty percent by weight of 1,6-diacetoxy- 3 wH CHr-COOCHPC=CHCHT-CHCHZOOCH3 35- LG-diacetoxy-B,5-dimethyl-2-hexeneacetic acid Both products resulting from Step 3 are pyrolyzed to form ahexadiene mixture, i.e., 2,5-dimethyl-2,4-hexadiene and2,5-dimethyl-1,5-hexadiene. The preferred thermal treatment temperatureis about 335 C. This pyrolysis is accomplished by passing the filteredproduct from the hydrogenation of Step 3 over a suitablealuminum-containing catalyst such as, for example, solid aluminumphosphate on alumina at a temperature of 250 C. to 375 C. with a contacttime of approximately seconds to 120 seconds. The preferred operatingtemperature is 335 C. with a period of contact of about seconds.

The resultant hexadiene mixture is separated from acetic acid producedin the reaction by a simple steam distillation. About 60 percent of thediene mixture is the desired 2,5-dimethyl-2,4-hexadiene. The remaining40 percent, which is the 1,5-isomer, referred to hereinabove, can beconverted to the desired 2,5-dimethyl-2,4- hexadiene by vapor-phaseisomerization over a chromealumina catalyst. This isomerization can beaccomplished alternatively by heating the 1,5-diene in the liquid phasewith a catalytic amount of a strong mineral acid, such as, preferably,sulfuric acid, para-toluenesulfonic acid, benzenesulfonic acid orsulfoacetic acid. Less preferred strong mineral acids which can beemployed are, for example, phosphoric acid, nitric acid, and hy drochlorc c d.

CH, CH. on.-d=ortorrr-onon,oooem 2,5-d1methyl-4-hexeny1 acetate CH; CH;0133COOCH,fJHCH=CH,CHCHrOOCCH; I 1,6-diacetoxy-2,5 dimethyl hexane E OCH; CH; cn ci=oncn=e em cmooorr g 2,5-dimethy1-2A-hexad1eue acetic acid7 CH; CH; CHF-( 'cH|CHl-=CH| 2011 0 0 0H 2,5-d1methy1-1,5-hex d1eneacetic acid Isomerization CH; CH; lVapor Phase CH;

or Acidic Catalyst in Liquid. Phase PROCESS 2 A novel alternate methodfor the preparation of 2,5- dirnethyl-2,4-hexadiene involves thesynthesis of methacrolein dimer (3,4-dihydro-2,S-dimethyl-Z-formyl-ZH-pyran) as described in Step 1 of Process I referred to hereinabove. Themethacrolein dimer can be hydrogenated at a pressure of 2500 to 5000psi. or preferably 4000 psi and temperatures of 140 C. to 350 C. using acopper chromium catalyst to. form 2,5-dimethy1-1,6- hexanediol a novelcompound. Alternatively, the dimer can be hydrogenated at a temperaturein the range of 40 C. to 160 C. and preferably about 100 C. using aRaney nickel catalyst at pressure of about 100 to 1000 psi. with apreferred pressure of about 150 psi. to form 2,5-dimethy1tetrahydropyran-Z-methanol, subsequent hydrogenol'ysis of which, at atemperature of about 225 C.

Catalyst to 400 C., or preferably 300 C., and apressure o'f2500 to5000'p.s.i.-, or again a preferred pressure of 4000 p;s.i., andemploying a copper-chromium-barium catalyst results in the formation ofthe diol; i.e., 2,5-dimethyl-L6-hexanediol, anovel compound. Acetylationof this diol. causes the production of l,6 diacetoXy-2,5-dimethylheXane.This hexane canthen be pyrolyzed as described above in Step 4 of Process1 to form substantially the same product mixture of2,5-dimethyl-2,4-hexadiene, 2, 5.-dimethyl 1',5- hexadiene and aceticacid described therein. The diene mixture is separated from the aceticacid produced in the reaction by a standard steam distillation, and the1,5- dieneproduct converted as described in Step 4' of Process 1 to thedesired 2.,4-diene isomer. Theprepara'tio'n of 1,6=diacetoxy-Z,S-dimethylhexane, pyroiysis. of which results in the dienemixture referred. to immediately hereinabo've, can be illustratedgraphically as follows:

acetic anhydride (CH COhO 2,5-dlmethyl-L6-hexanediol diacetate(1,6-diacetoxy-2,s-dlmethylhexane) CHgC 0 OH acetic acid2,5-dimethyl-2,4-hexadiene, prepared from the novel products of thisinvention, is an important starting material in the synthesis ofchrysanthemum acid chloride from which pyrethrin, a valuableinsecticide, can be synthesized. The series of steps necessary to thispreparation may be illustrated schematically as follows:

CH; OH;

2,l-dimethyl-2,4-hexadlene ethyl diazoacetate CH3 CH:

1 (1) NaOH CH; =CHCH-CCH; N:

(2) Mineral Acid (H;SO CH0 0 0 02115 chrysanthemum acid ethyl ether CH;CH!

CHr-C=CH-CHCCH thionyl cohlofide one 0 0H 2 chrysanthemum acid CH; CH!CH (=OHCH(JOH SO, -l- H01 C C 0 Cl chrysanthemum acid sulfer hydrogenchloride dioxide chloride The preparation of pyrethrin fromchrysanthemum acid chloride is described by La Forge and Barthel in theJournal of Organic Chemistry, vol. 12, pages 199 to 202 (1947).

It should be noted, in addition, that 2,5-dimethyl-1,6- hexanediol isalso of value in the preparation of esters which are of value asplasticizers, solvents and synthetic lubricants, and is of particularvalue when employed as an insect'repellant.

The following examples are further illustrative of our invention:

EXAMPLE 1 (a) A charge of 1000 grams (g.) of methacrolein (92 percent)and grams of hydroquinone was placed in a 3.1 stainless steel Adkinsbomb and heated to 140 C. for 16 hours while agitating by means of arocking mechanism in which the bomb was suspended. The initial pressurewas 195 p.s.i. and fell to 150 p.s.i. at the conclusion of the run.

The material was discharged after cooling and the unreacted methacroleinstripped off at atmospheric pressure. The distillation was continued atreduced pressure and 744 grams of3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran boiling at 50 C. at 10 mm.was obtained. Ahigh boiling residue remained which weighed 99 grams. Theyield to the dimer was 81 percent with an efficiency of 86 percent basedon the methacrolein charged.

(b) A charge of 1000 grams of methacrolein dimer prepared in theforegoing manner and 50 grams of commercial Raney nickel catalyst wereplaced in an Adkins bomb contained in a rocking mechanism andhydrogenated at 150 C. and 2000 p.s.i. hydrogen pressure. The materialwas discharged, filtered, and distilled. A total of 914 grams of2,5-dimethyltetrahydropyran-Z-metbanol boiling at 51 C./ 1.1 mm. wasobtained. This was a yield of 91 percent based on the dimer charged.

(c) A charge of 4000 grams of acetic anhydride, 567 grams of2,5-dimethyltetrahydropyran-Z-methanol and 8 grams of zinc chloride wereplaced in a distilling flask and refluxed for 11 hours at a kettletemperature of 140" C. At the end of the reflux period the acetic acidproduced in the reaction and the excess acetic anhydride were distilledoff to a head temperature of 69 C./4 mm. A small amount of2,5-dimethyltetrahydropyran-2-methanol acetate was collected as a headscut and 743 grams of 1,6-diacetoxy-2,S-dimethyl-Z-hexene boiling overthe range of 90 C./2 mm. to 110 C./1.0 was obtained as the mainfraction. A small tails cut containing 1,2,6-triacetoxy-Z,S-dimethylhexane was obtained. The total weight of the twoby-product esters was 88 grams. These materials are converted to thedesired unsaturated diester with good efiiciency, percent, by furtherreaction with acetic anhydride in the presence of the catalyst asdescribed immediately above.

The yield of the desired product was 81.3 percent and the efficiency89.9 percent based on the amount of methacrolein charged. I 1

The novel intermediate products prepared by this acetylation reactionwere characterized as follows:

1,2,6-triacetoxy-2,S-dimethylhexane:

Boiling point (B.P.)- C.l25 C./2 mm.;

Specific gravity (sp. gr.) at 20/20/ C.: 1.064;

Index of refraction (N 30/D)-1.43702,5-dimethyltetrahydropyran-Z-methanol acetate:

Sp. gr.-20/20 C.0.995;

N 30/D1.4420 1,6-diacetoxy-2,5-dimethyl-2-hexene Sp. gr.-20/20 C.-1.010;

(d) A charge of 1 652 grams of 1,6-diacetoxy-2,5-dimethyl-Z-hexene and33 grams of commercial Raney nickel catalyst were placed in an Adkinsbomb and hydrogenated at 50 C. and p.s.i. hydrogen pressure. Thereaction required 13 hours for completion. The product was dischargedand the catalyst filtered out. The reaction product was composed of 68grams of acetic acid, and the novel esters of 2,5-dimethyl-4-hexenylacetate (209 grams) and 1,6-diacetoxy-2,5-dimethylhexane (385 grams).

These novel compounds were determined to have the followingcharacteristics:

2,5-dimethyl-4-hexenyl acetate:

B.P.38 C./0.1 mm.; Sp. gr.-20/20 C.0.878; N 30/D-1.42141,6-diacetoxy-2,S-dimethylhexane:

B.P.-10l C./l mm.; Sp. gr.--20/20 C.0.986; N 30/D--1.4292

(e) The apparatus employed for this step in the process was a steel tube1 inch in diameter (I.D.) fitted with an electrically-wound jacketcontaining an oil by means of which the temperature could be maintainedat a constant level. The tube was charged with 340 cc. of a catalyst inthe following manner:

To 375 grams of activated alumina pellets (4 x 8 mesh) was added asolution of 450 grams of Al(NO .9H O in 300 cc. of water. This mixturewas allowed to reflux gently for 2 hours. The liquid was then drainedfrom the catalyst particles. A solution of 138 grams of diammoniumphosphate in 300 cc. of water was then added and the mixture was allowedto stand at 50 C. for 2 hours. The excess liquid was then drained 01fand the catalyst was dried overnight in a vacuum oven at 75 C.

A total of 674 grams of crude hydrogenation product as discharged fromthe bomb was fed over the catalyst at the rate of 50 cc./ hour while thejacket temperature was maintained at 335-340 C. A total of 615 grams ofliquid was obtained by passing the efiiuent gas through a water-cooledcondenser. This liquid was distilled to a kettle temperature of 52 C./25mm. A total of 588 grams of distillate was obtained While a high-boilingresidue of 15 grams remained behind. The distillate was then charged toa distilling flask and distilled with Water. The top layer was removedas distillate while the lower layer was returned to the kettle. A totalof 378 grams of upper layer was obtained while 301 grams of materialwhich contained 60.3 percent acetic acid remained in the kettle. Thedistillate was then fractionated and 296 grams of mixed2,5-dimethyl-1,S-hexadiene and 2,5-dimethyl-2,4-hexadiene was obtained.This represented a yield of 91.9 percent of the theoretical.Approximately 60 percent of the mixture of dienes was the. desired 2,4isomer.

The catalyst for the isomerization was prepared as follows:

Activated alumina pellets (500, grams of 4 x 8 mesh) were shaken with asolution of 50 grams of chromic acid in 250 cc. of Water for 20 minutes.The excess liquid was drained off and the catalyst was dried overnightat 120 C.

The reactor was a stainless steel tube 1% inches diam. and 4 feet inlength jacketed with an electrically-heated reservoir containing aheating oil. Five hundred cc. of catalyst prepared in the above mannerwas charged to the lower section ofthe reactor and the upper part wasfilled with 750 cc. of 4 x 8 mesh Aloxite (a commercial variety of fusedaluminum oxide). A flow of hydrogen was passed through the tube whilethe temperature was held at 425 C. for 5 hours.

A total of 886 gramsof 2,5-dimethyl-1,5-hexadiene was then fed at therate of 90 cc. per hour while the temperature was held at 220225 C. Thisprovided a contact time of 72 seconds for the vapors in the catalystzone.

The gas, effluent from the converter was condensed by passing through awater cooled condenser and a total of 882 grams were obtained. This wasfound to be 90 percent 2,5-dimethyl-2,4-hexadiene. The yield based onthe 1,5 isomer fed was 89.5 percent with an etficeincy of 95 .7.percent.

(f) A charge of 300 grams of 2,5-dimethyl-1,5-hexadiene, 1.5 grams ofpara-toluenesulfonic acid, and 0.5 gram tert-butyl catechol was placedin a flask equipped with a reflux condenser and heated for 3 /2 hours ata kettle temperature of 135 C. The product was distilled under reducedpressure and 250 grams of the desired 2,5- dimethyl-2,4-hexadiene wasobtained along with 40 grams of unchanged 1,5 diene. The yield to the2,4- isomer was therefore 83.2 percent and the efficiency 96.3. percent.

EXAMPLE 2 (a) [1] A mixture of 873 grams of2,5-dimethyltetrahydropyran-Zmethanol and 25 grams of barium promotedcopper chromite catalyst (Harshaw Chemical Company CU-O 4011 washydrogenated at 300 C. and 4000 pounds per square inch pressure for 6hours. The reaction product was filtered and distilled under reducedpressure to obtain 2,5-dimethyl-1,6-hexanediol having these properties:distillation range 117122 C./ 2.5 mm., sp. gr. 20/20 0.950, N 30/D1.4550, molecular Weight by the Menzies-Wright method 148.5 (theoretical146), equivalent weight by hydroxyl analysis 73.4 (theoretical 73). Theyield and efliciency were 45 percent and 83 percent respectively. Thiscolorless, viscous diol, which is a new compound, was approximately 5:percent soluble in water at 20 C.

(a) [2] A mixture of 1000 grams of methacrolein dimer and 30 grams ofcopper chromite catalyst (Harshaw Chemical Company Cu-0102-P) wasstirred in a 1 gallon autoclave under .3000 p.s.i. of hydrogen pressureat 140 C. After 30 minutes, the. absorption of hydrogen had ceased. Thetemperature and pressure were increased to 300350 C. and 4.000 p.s.i. tocomplete the reaction. After 5.5 hours under these conditions, theproduct was cooled, filtered and distilled. The2,5-dimethy1-1,6-hexanedio1 was obtained with 25 percent yield and 78percent efficiency.

(a) [3] A mixture of 1000 grams of methacrolein dimer and 50 grams ofRaney nickel was hydrogenated in a rocking, stainless steel bomb at 1500p.s.i. pressure and 78190 C. The temperature was then increased to 295300 C. with a pressure of 3500 p.s.i. for 5 hours. Thep roduct wasfiltered and distilled to obtain 2,5-dimethyl-1,6-hexanediol with a 10percent yield. The 2,3- dihydro-2,5-dimethy1-1,4-pyran-2-methanol was.formed with 85 percent yield.

(a) [4] A mixturev of 1964 grams of2,5-dirnethyltetrahydropyran-Z-methanol and 60 grams of copper-ironchromite was hydrogenated in an autoclave at 300-305 C. and 4000 p.s.i.for 6 hours. The product was filtered and distilled to obtain2,5-dirnethyl-1,6-hexanediol with 12 percent yield.

(b) While 568 grams of 2,5-dimethyl-1,6-hexanediol (3.89 moles) wereheated at. 140-160 C., 1588 grams of acetic anhydride (15.56 moles,percent excess) were added over a period of 30 minutes. The acetic acidwas then distilled to a head temperature of 134 C., and a kettletemperature of 186 C. The residue was fractionated under reducedpressure to obtain the diacetate having the following properties:boilingpoint 101 C. at 1 mm., N 30/D 1.4292, sp. gr. 20/20 C. 0.986,observed molecular weight 220 (theoretical 230), observed equivalentweight 118 (theoretical The yield and efiiciency were 99 percent basedon the diol. This colorless, water insoluble diacetate is a newcompound.

(0) A 1 inch stainless steel tube 3 feet long was packed with 450 cc. of4 x 8 mesh activated alumina catalyst. While the catalyst was heated at375 C., the diacetate was fed at the rate of 50 cc. per hour. Theproduct made from 228 grams of ester was fractionated under reducedpressure to obtain 91 grams of mixed 2,5-dimethylhexadienes. Analysis ofthe dimethylhexadiene fraction showed that 60 percent of it was2,5-dimethyl-2,4-hexadiene and the balance was2,5-dimethyl-1,5-hexadiene. The overall yield and efficiencyto thedimethylhexadienes was 83 percent. These 2,5-dimethylhexadienes wereseparated readily by either fractional distillation or by fractionalcrystallization. Since the 2,5-dimethyl-1,S-hexadiene is isomerized. tothe desired 2,5-dimethyl-2,.4-hexadiene by passing over activatedalumina catalyst or by an acid catalyst in the liquid phase, the formerdiene may be recycled. with the diacetate to the vapor phase, reactiontube to produce more 2,5 -dimethyl-2,4-hexadiene.

What is claimed is;

1. In a process for preparing an intermediate useful in they productionof allethrin, the step which comprises heating1,6-diacetoxy-2,5-dimethylhexane in the presence of aluminum phosphateas catalyst to cause the formation of 2,5-dimethyl-2,4-hexadiene.

2. In a process for preparing 2,5-dimethyl-2,4-hexadiene the steps whichinclude dimerizing methacroleinto form3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran; hydrogenating3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran in the presence of Raneynickel as catalyst to form 2,5- dimethyltetrahydropyran-Z-methanol;reacting 2,5.-dimethyltetrahydropyran-2methanol with acetic anhydride toform 2,5-dimethyl-1,6-diacetoxy-2-hexene; hydrogenating2,5-dimethyl-1,6-diacetoxy-2-hexene to produce a mixture composed of1-,6-diacetoxy-2,S-dimethylhexane and 2,5-dimethyl-4-hexenyl acetate;pyrolyzing said mixture to produce a composition containing2,5-dimethyl- 2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene.

3. In a process for preparing 2,5-dirnethyl-2,4-hexadiene the stepswhich include dimerizing :methacrolein to form3,4-dihydro-2,S-dimethyl-2-formyl-2H-pyran; hydrogenating3,4-dihydro-2,S-dimethyI-Z-formyl-ZH-pyran in the presence of Raneynickel as catalyst to form 2,5-dimethyltetrahydropyran-2-methanol;reacting 2,5-dimethyltetrahydropyran-Z-methanol with acetic anhydride toform 2,5-dimethyl-1,6-diacetoxy-2-hexene; hydrogenating2,5-dimethyl-1,6-diacetoxy-2-hexene to produce a mixture composed of1,6-diacetoxy-2-,5-dimethylhexane and: 2,5 dimethyl-4-hexenyl acetate;"pyrolyzing said mixture to produce a composition containing2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene and separating2,5- dimethyl-2,4-hexadiene therefrom.

4. In a process for preparing 2,5-dimethyl-2,4-hexadiene the steps whichinclude dimerizing methacrolein to form3,4-dihydro-Z,5-dimethyl-2-formyl-2H-pyran; hydrogenating3,4-dihydro-2,5-dimethyl-2-formyl-ZH-pyran in the presence of Raneynickel as catalyst to form 2,5411! methyltetrahydropyran-Z-methanol;reacting 2,5-dirnethyltetrahydropyran-2-methanol with acetic anhydrideto form 2,5-dimethyl-l,6-diacetoxy-2-hexene; hydrogenating 2,5-dimethyl-1,6-diacetoxy-2-hexene to produce a mixture composed of1,6-diacetoxy-Z,S-dimethylhexane and 2,5- dimethyl-4-hexenyl acetate;pyrolyzing said mixture to produce a composition containing2,5-dimethyl-2,4-hexa diene and 2,5-dimethyl-1,5-hexadiene and causingthe isomerization of 2,5-dimethyl-1,5-hexadiene to form 2,5-dimethyl-2,4-hexadiene.

5. In a process for preparing 2,5-dimethyl-2,4-hexadiene the steps whichinclude dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-2-formy1-2H-pyran; hydrogenating3,4-dihydro-2,S-dimethyI-Z-formyl-ZH-pyran in the presence of Raneynickel as catalyst to form 2,5-dimethyltetrahydropyran-2-methanol;reacting 2,5-dimethyltetrahydropyran-2-methanol with acetic anhydride toform 2,5-dirnethyl-1,6-diacetoxy-2-hexene; hydrogenating 2,5dimethyl-l,6-diacetoxy-2-hexene to produce a mixture composed of1,6-diacetoxy-2,5-dimethylhexane and 2,5-dimethyl-4-hexenyl acetate;pyrolyzing said mixture to produce a composition containing2,5-dimethyl-2,4-hexadiene and 2,5-dirnethyl-1,5-hexadiene and causingthe isomerization of said 2,5-dimethyl-1,5-hexadiene by pass ing said2,5-dimethyl-1,5-hexadiene in the vapor phase over a chromium-aluminumcatalyst to produce 2,5-dimethyl-2,4-hexadiene.

6. In a process for preparing 2,5-dimethyl-2,4-hexadiene the steps whichinclude dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-Z-formyl-ZH-pyran; hydrogenating3,4-dihydro-2,5-dimethyl-Z-formyl-ZH-pyran in the presence of Raneynickel catalyst to form 2,5-dimethyltetrahydropyran-Z-methanol; reacting2,5-dimethyltetrahydropyran-Z-methanol with acetic anhydride to form2,5-dimethyl-1,6-diacetoxy-2-hexene; hydrogenating 2,5-dimethyl-l,6-diacetoxy-2-hexene to produce a mixture composed of1,6-diacetoxy-2,5-dirnethylhexane and 2,6- dimethyl-4-hexenyl acetate;pyrolyzing said mixture to produce a composition containing2,S-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene and causingthe isomerization of 2,5-dimethyl-1,5-hexadiene by forming a mixture ofsaid 2,5-dimetl1yl-1,5-hexadiene and an acid catalyst therefore toproduce 2,5-dimethyl-2,4-hexadiene.

7. In a process for preparing 2,5-dimethyl-2,4-hexadiene the steps whichinclude dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran; hydrogenating3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran in the presence of Raneynickel catalyst to form 2,5-dimethyltetrahydropyran-Z-methanol; reacting2,5-dimethyltetrahydropyran-Z-methanol with acetic anhydride to form2,5-dimethyl-1,6-diacetoxy-2-hexene,2,5-dimethyltetrahydropyran-Z-methanol acetate and1,2,6-triacetoxy-2,5-dimethylhexane, continuing the reaction of2,5-dimethyltetrahydropyran-Z-methanol acetate and1,2,6-triacetoxy-2,S-dimethylhexane with acetic anhydride to cause theformation from these compounds of 2,5-dimethyl-l,6- diacetoxy-Z-hexene;hydrogenating 2,5-dimethyl-l,6-diacetoxy-Z-hexene to produce a mixturecomposed of 1,6- diacetoxy-2,S-dimethylhexane and 2,5-dimethyl-4-hexenylacetate; pyrolyzing said mixture to produce a composition containing2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene.

8. In a process for preparing 2,5-dimethyl-2,4-hexadiene the steps whichinclude dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl*Z-fOrmYI-ZH-pyran; hydrogenating3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran in the presence of Raneynickel catalyst to form 2,5-dimethyltetrahydropyran-Z-methanol; reacting2,5-dimethyltetrahydropyran-Z-methanol with acetic anhydride to form2,5-dimethyl-l,6-diacetoxy-2-hexene,2,5-dimethyltetrahydropyran-Z-methanol acetate and1,2,6-triacetoxy-2,5-dimethylhexane, continuing the reaction of2,5-dimethyltetrahydropyran-Z-methanol acetate and 1,2,6-triacetoxy-2,5-dimethylhexane with acetic anhydride to cause the formation fromthese compounds of 2,5-dimethyl1,6- diaCetoxy-Z-hexene; hydrogenating2,5-dimethyl-'1,6-diacetoxy-2-hexene to produce a mixture composed of1,6; diacetoxy-2,S-dimethylhexane and 2,5-dimethyl-4-hexenyl acetate;pyrolyzing said mixture to produce a composition containing2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene and separating2,5-dimethyl-2,4- hexadiene therefrom.

9. In a process for preparing 2,5-dimethyl-2,4-hexadiene the steps whichinclude dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran; hydrogenating3,4-dihydro-2,5-dimethyl-Z-formyl-ZH-pyran in the presence of Raneynickel catalyst to form 2,5-dimethyltetrahydropyran-Z-methanol; reacting2,5 -diinethyltetrahydropyran-Z-methanol with acetic anhydride to form2,5-dimethyl-1,6-diacetoxy-2-hexene,2,5-dimethyltetrahydropyran-Z-rnethanol acetate and 1,2,6-triacetoxy-2,5-dimethylhexane, continuing the reaction of2,5dimethyltetrahydropyran-Z-methan0l acetate and1,2,6-triacetoxy-2,S-dimethylhexane with acetic anhydride to cause theformation from these compounds of 2,5-dimethyl- 1,6-diacetoxy-2-hexene;hydrogenating 2,5dimethyl-l,6- diacetoxy-Z-hexene to produce a mixturecomposed of 1,6- diacetoxy-Z,S-dimethylhexane and 2,5-dimethyl-4-hexenylacetate; pyrolyzing said mixture to produce a composition containing2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl- 1,5-hexadiene and-causingthe isomerization of 2,5-dimethyl-1,5-hexadiene to form2,5-dimethyl-1,5-hexadiene to form 2,5-dimethyl-2,4-hexadiene.

10. In a process for preparing 2,5-dimethyl-2,4-hexadiene the stepswhich include dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran; hydrogenating said3,4-dihydro-2,5-dimethyl-2-formyl-2H- pyran to form2,5dimethyl-1,6-hexanediol; forming a mixture of2,5-dirnethyl-1,6-hexanediol and acetic anhydride to cause the formationof 1,6-diacetoxy-2,5-dimethylhexane; heating said1,6-diacetoxy-2,S-dimethylhexane sufficiently to cause the production ofa mixture containing 2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-l,5-hexadiene.

11. In a process for preparing 2,5-dimethyl-2,4-hexadiene the stepswhich include dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-Z-formyl-ZH-pyran; hydrogenating said3,4-dihydro-2,S-dimethyl-Z-formyl-ZH- pyran to form2,5-dimethyl-1,6-hexanediol; forming a mixture of2,5-dimethyl-1,6-hexanediol and acetic anhydride to cause the formationof 1,6-diacetoxy 2,5-dimethylhexane; heating saidl,6-diacetoxy-2,5-dimethyl hexane sutficiently to cause theproduction ofa mixture containing 2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadieue and separating 2,5-dimeth ,'l2,4-hexadiene therefrom.

12. In a process for preparing 2,5-dimethyl-2,4-hexadiene the stepswhich include dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran; hydrogenating said3,4-dil1ydro-2,5-dimethyl-2-formyl-2H- pyran to form 2,5-dimethyl-1,6-hexanediol; forming a mixture of2,5-dimethyl-1,6-hexanediol and acetic anhydride to cause the formationof l,6-diacetoxy-2,5-dimethylhexane; heating said1,6-diacetoxy-2,S-dimethylhexane sufiiciently to cause the production ofa mixture containing 2,5-dimethyl-2,4-hexadiene and2,5-dimethyl-1,5-hexadiene and causing the isomerization of2,5-dimethyl-1,5- hexadiene to form 2,5-dimethyl-2,4-hexadiene.

13. In a process for preparing 2,5-dimethyl-2,4--hexadiene the stepswhich include dimerizing methacrolein to form3,4-dihydro-2,5-dimethyl-2-formyl-2H-pyran; hydrogenating said3,4-dihydro-2,5-dimethyl-2-formyl-2H- pyran to'form2,5-dimethyl-1,6-hexanediol; forming a mixture of2,5-dimethyl-1,6-hexanediol and acetic anhydride to cause the formationof 1,6-diacetoxy-2,5-dimethylhexane; heating said1,6-diacetoxy-2,5-dimethylhexane sufficiently to cause the production ofa mixture containing 2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene and causing the isomerization of2,5-dimethyl-2,4-hexadiene by forming a reaction mix of said2,5-dimethyl-1,S-hexadiene and an acid catalyst therefor to produce2,5-dimethyl-2,4-hexadiene.

14. In a process for preparing 2,5-dimethyl-2,4-hexadiene the stepswhich include dimerizing methacrolein to form3,4-clihydro-2,5-dimethyl-Z-formyl-ZH-pyran; hydrogenating said3,4-dihydro-2,5-dimethyl-2-formyl-2H- pyran to form2,5-dimethy1-1,6-hexanediol; forming a mixture of2,5-dimethyl-1,6-hexanedio1 and acetic anhydride to cause the formationof 1,6-diacetoxy-2,5-dimethylhexane; heating said1,6-diacetoxy-2,5-dimethylhexane sufi'iciently to cause the productionof a mixture containing 2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene; distilling 2,5-dimet'nyl-2,4-hexadiene from said mixtureand causing the iscmerization of 2,5'-dimethyl-2,4-hexadiene by forminga reaction mix of said 2,5-dimethyl-1,5-hexadiene and an acid catalysttherefor to produce 2,5-dimethyl-2,4-hexadiene.

References Cited in the file of this patent UNITED STATES PATENTS2,097,493 Leuck et al. Nov. 2, 1937 2,204,157 Semon June 11, 19402,224,912 Hill et a1. Dec. 17, 1940 2,251,983 Chitwood Aug. 12, 19412,345,113 Guggemos et a1 Mar. 28, 1944 2,391,509 Pines et a1. Dec. 25,1945 2,412,762 Workman Dec. 17, 1946 2,479,283 Whetstone Aug. 16, 19492,527,120 Denivelle Oct. 24, 1950 2,692,892 Hillyer et a1 Oct. 26, 19542,715,649 Hammond Aug. 16, 1955 2,774,771 Longley Dec. 18, 1956 FOREIGNPATENTS 451,827 France Feb. 21, 1931 OTHER REFERENCES Schneipp et a1.:Jour. Amer. Chem. Soc., vol. 67, pages 54 1945 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 2,910,520 October 27, 1959Howard R. Guest et a1.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 2 line 3, for "is" read of column '3, lines Z1 to 73, left-handportion of the formula, for:

CH CH CH C= read CH C= column 7, line 62., for "'56?" read 576 column 8,line 12,, for read 20 C, column 9, line 71 for "Thep roduct" read Theproduct Signed and sealed this. 30th day of August 1960.

(SEAL) Attest:

ERNEST W, SWIDER Attesting Officer R BERT C. WATSON Commissioner ofPatents

1. IN A PROCESS FOR PREPARING AN INTERMEDIATE USEFUL IN THE PRODUCTIONOF ALLETHRIN, THE STEP WHICH COMPRISES HEATING1,6-DIACETOXY-2,5-DIAMETHYLHEXANE IN THE PRESENCE OF ALUMINUM PHOSPHATEAS CATALYST TO CAUSE THE FORMATION OF 2,5-DIMETHYL-2,4-HEXADIENE.